Data from: Are extra-pair males different from cuckolded males? An empirical and meta-analytic examination

Traditional models for female extra-pair matings assume that females indirectly benefit from extra-pair mating behavior. Under these so-called “adaptive” models, extra-pair males are hypothesized to have more compatible genotypes, larger body size, exaggerated ornaments, and be older than cuckolded males. Alternatively, models that consider female extra-pair matings as a by-product (”non-adaptive”) posit that female extra-pair mating can be maintained regardless of female fitness consequences. This would be the case, for example, if males benefit from extra-pair mating behaviour and female and male behaviour are genetically correlated. Extra-pair males could also be expected to be older and larger if this makes them better at convincing and coercing females to mate. We investigated whether a female’s extra-pair mates are different from her cuckolded mate in both genetic and phenotypic traits by analysing data from the Lundy house sparrow population. We found that extra-pair male sparrows were older than cuckolded males, in accordance with both models. However, extra-pair and cuckolded males are of similar genetic compatibility with the female, and have comparable body size and secondary sexual traits. We also updated previous meta-analyses examining differences between extra-pair and cuckolded males. The meta-analytic results largely matched results from the house sparrow data. We discuss that, although we cannot completely exclude indirect benefits for females, non-adaptive models may better explain female extra-pair matings. These neglected alternative models deserve more research attention than they currently receive.